Well if you can track it down in your order history (not the easiest thing to do I’ll admit) it might help work out if it was part of another bundle or something. Sadly the email doesn’t really confirm anything, since it went out in part in error.
From what I’ve heard everyone else with either the original Marrakesh Souks, or the Marrakesh Anniversary Bundle got the discount ok. So I guess you didn’t purchase either other them..as far as I can recall, I don’t think it was part of any of bundle. Again, support should be able to help out though, I’m sure they can look at your account and see what you’ve purchased.
Sorry I can’t be of more help.